This invention relates generally to thermal engines and is particularly concerned with an improved construction for such an engine, particularly a Stirling engine.
In an example of a Stirling engine a swashplate is journaled for rotation on a housing. The swashplate is driven by crossheads connected to reciprocating pistons and the swashplate in turn operates a drive shaft via which mechanical power is delivered to any utilization mechanism coupled to the engine. The construction of the drive mechanism is such that forces which act on the swashplate are at locations spaced from the axis of rotation of the swashplate. It has been observed that the interaction of the drive mechanism with the swashplate is such that each force component acting on the swashplate is resolved into a component producing rotation and a component which tends to impart bending to the drive shaft.
In the example, the Stirling engine includes a pressure hull cooperatively associated with the engine housing to define an interior space which is subject to pressures different from those on the exterior of the pressure hull, i.e. on the outside of the engine. The drive shaft passes through both the housing and the pressure hull so that power can be delivered to whatever utilization mechanism is connected to the engine.
Stirling Thermal Motors, Inc., assignee of the present invention, has been involved in development work on such engines and has heretofore created an improved mounting and sealing of the pressure hull on the engine housing. The present invention is directed to a further improvement for enhancing the effectiveness of the seal between the drive shaft and the housing and which also incorporates, in the peferred embodiment, the benefits of the previous improvement in construction of the pressure hull.
More specifically the present invention arises through the recognition that the bending of the drive shaft which is caused by one of the components of force applied to the swashplate can impair the effectiveness of the pressure seal which is required between the drive shaft and the housing. The present invention responds to this observation by providing a novel and unique construction wherein the drive shaft is constructed of two separate drive shaft members operatively coupled together. One of these members is coupled to the swashplate and is so journaled on the housing that the bending moment imparted to the drive shaft by the swashplate is reacted substantially entirely via this first shaft member and its journaling on the housing. The second shaft member is also journaled on the housing, and the pressure seal between the drive shaft and the housing is provided between this second shaft member and the housing. The point of operative coupling between the two shaft members is between the pressure seal and the swashplate. The illustrated form of operative coupling in the disclosed example is a spline connection between the two shaft members. With this construction the bending loads are not transmitted through to the second shaft member so that the pressure seal is not subjected to any significant side forces. Hence, effectiveness of this seal is significantly improved. The construction provides further advantages of having convenient assembly and disassembly, and a further pressure seal between the pressure hull and the housing is also unaffected by the drive shaft bending.
The foregoing features, advantages and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a preferred embodiment of the invention according to the best mode contemplated at the present time in carrying out the invention.